1. Field of the Invention
The invention relates to a fuel injector.
By use of a fuel injector, metered quantities of fuel are injected into a combustion space of an internal combustion engine. In future common-rail injection systems, the fuel is to be injected at a pressure of well above 1000 bar, and therefore the aim is to configure fuel injectors so as to be particularly suited to high pressures.
International Patent Disclosure WO 00/60233 discloses a fuel injector that has a first injector module and an adjoining second injector module. The injector modules are disposed in a nozzle tension nut. A high-pressure bore is led through the injector modules. So that, because of the high pressure in the high-pressure bore, no fuel emerges through the gaps formed by contact surfaces between the injector modules into the gaps formed by contact surfaces between the nozzle tension nut and the injector modules and leaks from there into the surroundings of the fuel injector. The injector modules are pressed onto one another with a high axial prestressing force by the nozzle tension nut.
The surface pressure is particularly high, since at least one of the contact surfaces has an elevated part surface in the outer region, so that the entire prestressing force acts only on the part surface. The elevated part surface prevents the fuel from emerging into the gap formed by contact surfaces between the nozzle tension nut and the injector modules. Located in the inner region of the contact surface is a sunken part surface that is connected to a return bore for the discharge of fuel emerging from the high-pressure bore.
In order to seal off the fuel injector by the measures described, very high prestressing forces are necessary. The height of the permissible prestressing forces is limited, however, by the material strength of the nozzle tension nut and of the injector modules. Prestressing forces that are too high may lead to material damage or operating faults of the fuel injector. Thus, components lying in the force flux and having narrow guide clearances, such as, for example, the nozzle needle and control piston, could jam.
It is accordingly an object of the invention to provide a fuel injector which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which has higher high-pressure tightness along with lower prestressing forces.
With the foregoing and other objects in view there is provided, in accordance with the invention, a fuel injector. The fuel injector contains a housing having at least one return bore. The housing includes at least one nozzle tension nut with a nut contact surface, a first injector module having a first contact surface, and a second injector module having a second contact surface. The first injector module and the second injector module adjoin one another and are disposed in the nozzle tension nut. The first injection module and the second injector module have at least one high-pressure bore leading through the first injection module and the second injector module for conducting fuel. The first contact surface and the second contact surface have a first space formed there-between defining a first gap adjoining the high-pressure bore. The nut contact surface and the first contact surface have a second space formed there-between, and the nut contact surface and the second contact surface have a third space formed there-between. The second space and the third space together define a second gap connected to the first gap. The second gap is sealed off relative to surroundings of the fuel injector. The return line adjoins the second gap for discharging the fuel that has entered the second gap from the high-pressure bore through the first gap.
There is therefore no attempt to prevent completely the leakage of fuel out of the first gap. Instead, a leakage out of the second gap is prevented, in that the second gap is sealed off relative to the surroundings of the fuel injector and pressure is prevented from building up in the second gap with the aid of the return bore.
Since high-pressure tightness is achieved not solely by the injector modules being pressed onto one another, the prestressing force with which the injector modules are pressed against one another can be within a range which is harmless to the material strength of the injector modules and of the nozzle tension nut.
The high high-pressure tightness is achieved without any enlargement of the construction space.
The second gap can be sealed off, for example, with the aid of an O-ring seal. The O-ring seal is disposed, for example, between the nozzle tension nut and the first injector module.
A screw connection coated, for example, with Teflon may also be used for sealing off the second gap. Particularly good sealing off can be achieved by the screw connection being coated with a microencapsulated adhesive or sealant. During screwing, the capsules break open and release the adhesive or sealant.
Surface pressure may also contribute to sealing off the second gap. For example, the nozzle tension nut has a projection, against which an injector module is pressed with an axial prestressing force.
The return bore may be formed at least of a main bore and of an adjoining relief bore, the main bore running essentially perpendicularly to the contact surfaces between the injector modules, and the relief bore emerging laterally from the second injector module into the second gap.
Since a groove can be produced more simply in comparison with a bore, it is advantageous if the return bore is formed at least of a main bore and of an adjoining relief groove, the main bore running essentially perpendicularly to the contact surfaces between the injector modules, and the relief groove being introduced onto at least one of the contact surfaces between the injector modules, in such a way that the relief groove adjoins the second gap.
It is within the scope of the invention to provide further injector modules, through which the high-pressure bore is led and which are disposed in the nozzle tension nut. In this case, too, leakage through gaps formed at the contact surfaces between the injector modules is not critical, since the gaps, like the first gap, issue into the second gap that is sealed off relative to the surroundings of the fuel injector and is connected to the return line.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a fuel injector, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.